The invention relates to luminal endoprostheses for ramifications (also called branchings or bifurcations) of anatomical conduits in mammals, especially humans.
The endoprosthesis according to the invention concerns more especially the vascular system and the cardiovascular system where, at various sites, there are branchings, ramifications or bifurcations, the essential function of which is to provide a balanced supply of blood to the organs, muscle tissues and connective tissues.
The circulation of the blood in the vessels raises numerous problems associated with hydrodynamics and due to the structure and, in general, the shape of these vessels.
Physiologists and morphologists generally accept that the disposition of the vessels is such that the circulation necessitates, mechanically, a minimum level of stress and that the surface of the walls adopts a minimum value.
The luminal endoprostheses which have been developed to date generally assume simple tubular or cylindrical shapes or, more rarely, a hyperboloid shapes. Such prostheses are described in particular in the documents WO-A-83/03752 and GB-A-1 205 743.
These prostheses include a tubular braided structure for an arterial conduit or other conduit and are put into place, after compression of their diameter, using a tubular applicator. These prostheses are not intended for implantation in a bifurcated shape.
Attempts have been made to develop bifurcated shapes of prostheses. These essentially concern the junction of the abdominal aorta, which is a large vessel, but investigations are in their infancy.
A bifurcated prosthesis for implantation in a conduit such as a blood vessel is known, in particular, from U.S. Pat. No. 4,994,071.
This prosthesis, made up of interconnected metal rings, comprises a trunk formed by a first series of interconnected rings, and at least one branch formed by a second series of interconnected rings, these at least two series being connected to each other via a flexible element, folded in such a way as to correspond to the angle between the ramifications in question. Putting such a prosthesis into place is extremely difficult, or even impossible.
U.S. Pat. No. 5,609,605 describes a bifurcated endoprothesis made out of two single balloon endoprostheses of variable diameter placed side-by-side in a bifurcated lumen.
Documents EP-A-0 539 237 and WO 96/34580 describe devices for putting bifurcated endoprostheses into place. These endoprostheses include a main body (trunk) and two members (branches) extending from the main body; they are made of woven, folded or pleated fibre. Placing such endoprostheses in arterial bifurcations is a long and delicate operation, especially on account of stringent requirements in respect of orientation and positioning. Furthermore, the angle provided by the two branches does not necessarily correspond to the original angle between the vessels.
Document EP-A-0 461 791 illustrates the difficulties involved in putting a bifurcated prosthesis into place, even in the case of an aneurysm of the abidominal aorta, where the vessels are of a large diameter.
Other documents as U.S. Pat. Nos. 5,609,627 and 5,639,278 describe trouser-form endoprotheses with added legs, which often cause blood flow perturbation.
The bifurcation anglers differ from one person to the next and from one population to another. They are smaller and more asymmetrical in the elderly than in younger subjects. The bifurcations are more asymmetrical in men than in women. Comparative studies have shown that the bifurcation angles in Asiatics are wider than in Caucasians.
Hydrodynamics also teaches that the thicknesses of the arterial walls differ from one population to another. When these walls are thin, the effort necessitated by the transport of the blood increases. It is also known that when the vessels are too large, the volume of blood increases beyond what is necessary. These factors promote aneurysms (dilation of the arterial wall).
The considerations detailed above show that it would be necessary to adapt the design of a bifurcation to each anatomical site, and also that this design must take into account the differences between different types of populations, between men and women, between the young and the elderly, etc. In practice, it is not possible to provide bifurcations tailored to each patient. This would in fact risk causing problems associated with waiting periods and prohibitive costs.
It has therefore been sought to develop a luminal endoprosthesis which can adapt to practically all the ramifications of the anatomical conduits, and in particular to those of the vascular and cardiovascular system.
Another object of the invention is that this endoprosthesis should be easy to put into place.
Another object is to afford the possibility of placing such an endoprosthesis at sites which have hitherto been inaccessible.
The subject of the invention is a luminal endoprosthesis for ramification of an anatomical conduit, including at least one radially compressible and extendable tubular structure which comprises at least one base element comprising a continuous multifilament structure with N filaments delimiting a longitudinal cavity open at its two ends. This at least one base element comprises two flexible segments, respectively a first segment and a second segment, extending one in a continuation of the other, substantially along the same axis in the absence of stress, and at least one lumen opening into the longitudinal cavity at the junction between the first segment and the second segment, the same metal filaments forming the structure of the first segment and of the second segment.
According to a first preferred embodiment, the first element (or trunk) has a greater cross-section than that of the second segment (or branch). According to a second preferred embodiment, the first segment and the second segment of one base element have cross-sections which are practically identical.
This endoprosthesis generally comprises two base elements, the respective first segments of each of these two base elements being able to be engaged one within the other, and assuming, in this position, cross-sections which are in essence identical, the second segment of one of the base elements being engaged in a lumen of the other base element.
At least one of the base elements advantageously comprises a sleeve made of biocompatible material, such as a polymer of the polyester, polyurethane or polyethylene type, or another type of biocompatible material.
The structure of each base element can be braided using metal filaments made of an alloy for medical use or shape-memory filament.
The first segment of each of the two base elements can comprise a part of greater cross-section.
According to one embodiment, the second segment of at least one of the base elements comprises a part of greater cross-section. In the absence of stress, the filaments of the braided structure intersect at an angle and a diameter which vary depending on the desired application.
In a preferred manner, the cross-section of the trunk of a base element is equal to at least 4 times that of its branch and/or a lumen of a base element has a cross-section at least equal to xc2xc that of the trunk or at least equal to that of the branch.
Another subject of the invention is a method for manufacture of braided multifilament structures for an endoprosthesis as described herein above, and which method comprises the following operations:
braiding of filaments, made of a biocompatible elastic, shape-memory or superelastic material, around a first mandrel, along the length and the diameter corresponding to the branch of a base element,
setting up at least one auxiliary mandrel parallel to the first mandrel, the said auxiliary mandrel including a first end and a second end, of cross-section corresponding to those of a lumen, the said first end being inserted in a straight line with the braid in progress, upstream of the braiding point, the assembly (first mandrelxe2x80x94auxiliary mandrel) having a cross-section corresponding to that of a trunk of a base element,
continuing the braiding around the assembly along a length corresponding to at least that of the trunk of a base element.
This method may additionally comprise the following operation:
continuing the braiding around the assembly (first mandrexe2x80x94auxiliary mandrel) along a length corresponding to at least twice that of the trunk of a base element,
separating the second end of the at least one auxiliary mandrel from the first mandrel, the said second end having a cross-section corresponding to that of a lumen of a base element,
continuing the braiding on the first mandrel, along a length and a diameter corresponding to the branch of a base element,
disengagement of the obtained braid and of the mandrels,
cutting the obtained braid into two distinct base elements.
When the auxiliary mandrel comprises at least one flexible part, the separation between the second end of the auxiliary mandrel and the main mandrel can be effected by folding down the said second end on the braid in progress.
In addition, at least one widening part can be placed on the said first mandrel along the length corresponding to one of the future branches.
A widening part, of diameter greater than the assembly (first mandrelxe2x80x94auxiliary mandrel), can be placed on this assembly along the length corresponding to the future trunks. The method of manufacture, such as described, can comprise the insertion of a single auxiliary mandrel or of two auxiliary mandrels.
The invention also relates to a method for manufacture of braided multifilament structures for the base element of an endoprosthesis such as described herein above, which method comprises the following operations:
braiding of filaments, made of biocompatible elastic, superelastic or shape-memory material, around a first mandrel, along the length and the diameter corresponding to one of the segments of the base element,
setting up an auxiliary mandrel perpendicular to the first mandrel, the said auxiliary mandrel having a cross-section corresponding to those of the desired lumen of the said auxiliary mandrel, the said auxiliary mandrel being inserted at the level of the braiding point of the braid in progress,
continuing the braiding around the assembly (first mandrelxe2x80x94auxiliary mandrel) along a length corresponding at least to that of the contact (first mandrelxe2x80x94auxiliary mandrel),
continuing the braiding on the first mandrel, along a length corresponding to the other segment of the base element,
disengagement of the obtained braid and of the first mandrel. The setting up of an auxiliary mandrel is advantageously repeated during the braiding of the element in such a way as to form several distinct lumens.
When shape-memory filaments are used, the above operations are completed by the thermal operations required for the metal to memorize a predetermined nominal shape.
An advantage of the endoprosthesis according to the invention is that it adapts to virtually any type of branching or ramification, particularly of the arterial system, and to any angle, and this irrespective of the age and sex of the subject and the population to which the subject belongs; it is thus universal.
The developed endoprosthesis shape is simple and flexible, and it thus matches the anatomical site as it is, by which means it is possible to avoid the problems of positioning, migration, thrombosis and adaptation to the geometry of the original ramification of each patient.
The endoprostheses according to the invention can be made with numerous variations in terms of cross-section, length, and angle of intersection of the filaments, and they can be made of numerous materials.
The endoprostheses according to the invention can be made on machines currently used for obtaining traditional tubular endoprostheses.